/* $Header: crc16.c,v 2.2 01/10/02 10:32:10 przybyls Exp $ */
/*
 * hpfcla:net.sources / hcrvax!sft /  8:17 pm  Nov 15, 1984
 * The following program is a command to calculate the CRC of files.
 * It is useful for the same purposes as sum(1).  It calculates the
 * true CRC16 (unlike CP/M utilities that say they calculate CRCs
 * but really just hash).  Crc detects more errors than old sum(1);
 * for example, it detects exchanges of characters.  It is also
 * (now) in the public domain.
 *
 * Usage: crc [file ...]
 *
 * Calculate CRC16 of a file.
 * CRC16 polynomial: x**0 + x**2 + x**15 + x**16 (0xA001)
 * (CCITT polynomial: x**0 + x**5 + x**12 + x**16 (0x8408))
 * Initial condition: 0
 *
 * There are really two programs.  The first (compiled with
 * "TABLE" defined) calculates CRC tables to be included
 * in the second (compiled without "TABLE").
 *
 * D. Hugh Redelmeier  1983 April 15
 * Latest change: 1984 April 2.
 *
 * Test data (ref: EMBEDDED SYSTEMS PROGRAMMING, Jan 1992, page 33)
 * "M"                                  35c0
 * "T"                                  ff01
 * "THE"                                23b6
 * "THE,QUICK,BROWN,FOX,0123456789"     b96e
 *
 * Changed output format to be more like wc and did other cleanup (ajs 841212).
 * Minor cleanup + replaced second program with function call (jsd 920804).
 */

#ifdef TABLE  /* standalone program to generate table */

#include <stdio.h>

main()
{
        register unsigned s, t;
        register int i;

        printf("unsigned short CRCtab[256] =\n{");
        for (t = 0;;)
        {
                if (t % 8 == 0)
                        printf("\n");
                s = t;
                for (i = 8; i--;)
                        s = s >> 1 ^ (s & 1 ? 0xA001 : 0);
                printf("\t0x%04x", s);
                if (++t == 256)
                        break;
                printf(",");
        }
        printf("\n};\n");
}

#else  /* function to return CRC */

#include <typedefs.h>
#include <error.h>
#include <method.h>

/* CRC table & function must both be in boot ROM for ROM checksums in startup.c */
#ifndef mccabe
#pragma SECTION PROG=boot
#pragma SECTION CONST=boot
#endif

static unsigned short const CRCtab[256] =
{
        0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241,
        0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
        0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
        0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
        0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
        0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
        0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
        0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
        0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
        0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
        0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
        0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
        0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
        0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
        0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
        0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
        0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
        0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
        0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
        0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
        0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
        0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
        0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
        0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
        0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
        0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
        0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
        0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
        0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
        0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
        0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
        0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040
};

U_INT16 crc16(register U_INT8 *bytes, register INT32 len)
{
        register unsigned s;    /* CRC accumulator */

        s = 0;

        for (; len--;)
        {
                s = CRCtab[(s & 0xFF) ^ *bytes++] ^ (s >> 8);
        }

        return (U_INT16) s;
}

U_INT16 AddToCrc( U_INT8 data, U_INT16 crc )
{
    return CRCtab[ ( crc & 0xff ) ^ data ] ^ ( crc >> 8 );
}

#ifndef mccabe
#pragma SECTION UNDO
#pragma SECTION UNDO
#endif

#endif
